The invention relates to a controlling system and to a method for operating a controlling system having a controller which acts on a controlled system with the aid of a manipulated variable as a function of a number of controller parameters.
A technical plant usually has a number of controlling systems whose purpose is to ensure an undisturbed operation of the plant. Such a controlling system usually acts on an associated controlled system so as to produce a closed control loop. In this case, for example, a sensor at the measuring point of the controlled system measures the controlled variable to be observed. If, due to a disturbance variable, the controlled variable deviates from a prescribed desired value, the controller of the controlling system acts with the aid of its manipulated variable on an actuator assigned to the controlled system. The manipulated variable supplied by the controller depends in this case on the deviation of the measured controlled variable from the prescribed desired value and further depends on a number of controller parameters via which it is possible, for example, to set the reaction rate and/or the setting accuracy of the controller.
Because of a lack of systematic knowledge of the real dynamic response of the controlled system, the setting of the controller parametersxe2x80x94the so-called parameterizationxe2x80x94of such a controller is usually based on empirically obtained data which are determined, for example, when the plant is put into operation. These data are used to prescribe, for the respective controller, controller parameters which are retained unchanged during further operation. However, in the case of such a controlling system, a variation in the properties of the controlled system can lead to an impairment or deterioration of the control quality, in particular to impairment of the setting accuracy and/or of the rate of reaction of the controller. variations in the properties of the controlled system can occur in this case, in particular, from a change in load point or a change in the machine characteristic, for example because of aging or pollution.
The book by O. Vxc3x6llinger, Regelungstechnik [Control engineering], 6th edition, Huttich Buchverlag Heidelberg, 1990, Chapter 1.6, pages 14 to 20, discloses an adaptive control method in which the variable system performance caused by fluctuating parameters of the controlled system is firstly detected in a suitable way, and the controller parameters are fixed with the aid of the information thus obtained.
Furthermore, U.S. Pat. No. 5,610,843 discloses the use of wavelet transformations for the purpose of characterizing controlled systems. The use of wavelet transformations is also discussed in Japanese Patent Application JP 09120303.
Furthermore, German Patent DE 34 45 791 discloses a steam turbine generator system in which the vapor pressure and the temperature can be controlled.
The article entitled xe2x80x9cSelf-tuning control of nonlinear systems using neural network adaptive frame waveletsxe2x80x9d, which was published in the 1997 International Conference on systems man and cybernetics, volume 2, Oct. 12, 1997, pages 1017-1022, describes a special neural network with the aid of which a dynamically varying plant operation can be controlled. In accordance with the mathematical model presented therein, a wavelet transformation of an input function is performed for the process. This wavelet transformation is a basis for estimating an output function. The estimated output function is optimized by iteration steps by comparing the estimated output function with a measured output function, in order to be able to control the plant suitably.
It is accordingly an object of the invention to provide a method for operating a controlling system, which maintains the control quality and control response of the control loop even in the case of a variation in the properties of the controlled system. It is a further object of the invention to provide a controlling system having an improved control quality and control response.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for operating a controlling system, the method includes the steps of:
acting, with a controller of a controlling system, on a controlled system by using a manipulated variable, the controller acting in dependence of a plurality of controller parameters;
determining a response characteristic of the controlled system during operation of the controller by comparing a wavelet transformation of a temporal response of the manipulated variable with a wavelet transformation of a temporal response of a controlled variable of the controller in a given time window;
ascertaining respective instants assigned to the wavelet transformation of the temporal response of the manipulated variable and to the wavelet transformation of the temporal response of the controlled variable; and
setting at least one of the controller parameters as a function of the response characteristic.
In other words, the object of the invention is achieved by virtue of the fact that the response characteristic of the controlled system is determined in a prescribable time window during operation of the controller by comparing a wavelet transformation of the temporal response of the manipulated variable with a wavelet transformation of the temporal response of a controlled variable of the controller of the controlled system, an instant assigned to the respective wavelet transformation being detected, and the or each controller parameter being set as a function of the response characteristic determined.
The invention is based on the consideration that in the event of a change in the properties of the controlled system, the control quality and the control response of the control loop are maintained even when the variation in the response of the controlled system is detected and used to adapt the controller parameters. The response characteristic of the controlled system is particularly suitable in this case for characterizing the controlled system. A variation in the response characteristic of the controlled system should therefore act on the controller parameters. In order to avoid impairment of the functionality of the controlled system, in this case the resetting of the controller parameter or parameters is performed as a function of the determined response characteristic of the controlled system in the manner of an online intervention during operation of the controller.
A wavelet transformation is used in this case to determine the response characteristic of the controlled system during operation of the controlling system. In this case, the temporal variation of the manipulated variable and of a controlled variable of the controller of the controlled system are analyzed in the same way in a prescribable time window with the aid of a wavelet transformation. The method of wavelet transformation is described, for example, in the journal Automatisierungstechnik [automation technique], edition 2, 1996, R. Oldenbourg publishers, pages 64 to 66.
With this analysis it can be established whether a prescribable component of the manipulated variable is included in the controlled variable. This is performed by decomposing the manipulated variable or the control variable into components of a so-called wavelet family in a prescribable time window at a specific instant or point in time. A wavelet family is a family of mathematical functions which are generated by mathematical stretching and/or displacement from a single output function. The mathematical stretching and/or displacement of the function in this case signifies adaptation to various frequency and amplitude components of a signal to be investigated. The time when the variable to be investigated has specific properties can be determined in this case on the basis of the presence of prescribable wavelet components within the framework of the prescribable time window.
The response characteristic of the controlled system is determined in this case by comparing the wavelet transformation of the temporal response of the manipulated variable with the wavelet transformation of the temporal response of the controlled variable. For this purpose, the result of the analysis of the manipulated variable and of the controlled variable is transferred into a system of differential equations. The formulation of the system of differential equations serves to establish a mathematical function which characterizes the response characteristic of the controlled system.
An instant assigned to the wavelet transformation is detected with each determination of the response characteristic of the controlled system. It is thereby possible to document changes in the response characteristic of the controlled system. It is possible in this way for the controlling system to be adapted particularly simply to prescribable operating states of the controlled system which keep reoccurring during operation of the controlled system.
The method is advantageously applied to a controlling system which is part of a steam turbine plant. Specifically, the controllers of the control loop of a steam turbine plant are usually parameterized with the aid of empirically obtained data. Because of a lack of systematic knowledge of the real dynamic response of the respective steam turbine plant, long commissioning times occur in this case. Again, as a rule the controller parameters are not adapted to different operating states of the steam turbine plant during operation of the steam turbine plant. Readjusting or tracking of the controller parameters of the or each controller of the steam turbine plant during operation of the steam turbine plant therefore ensures particularly a constant control quality and a constant control response of the or each control loop.
The manipulated variable of the controller is advantageously a wheel chamber pressure value or a steam mass flow value of the steam turbine. In an advantageous embodiment, the controlled variable of the control loop is, furthermore, a power value, a speed value or a pressure value of the working medium of the steam turbine.
With the objects of the invention in view there is also provided, in combination with a controlled system having a response characteristic, a controlling system, including:
a controller connected to the controlled system, the controller operating in dependence of a plurality of controller parameters, and the controller acting, with a manipulated variable, on the controlled system;
a controller adaption device connected to the controller;
the controller adaption device determining the response characteristic of the controlled system during operation of the controller by comparing a wavelet transformation of a temporal response of the manipulated variable with a wavelet transformation of a temporal response of a controlled variable of the controller in a given time window;
the controller adaption device ascertaining respective instants assigned to the wavelet transformation of the temporal response of the manipulated variable and to the wavelet transformation of the temporal response of the controlled variable; and
the controller adaption device setting at least one of the controller parameters as a function of the response characteristic.
In other words, the object of the invention is achieved with the aid of a controller adapter which determines the response characteristic of the controlled system during operation of the controller, and sets the or each control parameter as a function of the currently determined response characteristic of the controlled system.
The advantages achieved with the invention are, in particular, that by readjusting or directing the controller parameters in the sense of an auto-tracking during operation of the controller ensures a given control quality for all operating states of the controlled system. This is performed without interrupting the operation of the controlling system. Moreover, technical plants which include the controlling system and apply the method have particularly short commissioning times when the plant is put into operation.
Again, controlling systems operated with the aid of the method according to the invention can be adapted with particular ease to different operating states of the controlled system.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for operating a controlling system, and a device for carrying out the method, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.